1. Field of the Invention
The present invention relates to circuitry for extending the harmonic content of a computor organ of the type disclosed in U.S. Pat. No. 3,809,786, and particularly to the use of such extended harmonic circuitry in the generation of tones having the spectral shape of a sawtooth wave.
2. Description of the Prior Art
The computor organ disclosed in U.S. Pat. No. 3,809,786 enables the generation of a very wide range of musical waveshapes. This is accomplished by a Fourier synthesis technique in which the individual Fourier components of the waveshape are calculated separately and combined to obtain, in real time, the consecutive sample point amplitudes of the generated waveshape. Complete control of the spectral content thus is achieved, since the relative amplitude of each Fourier component is individually selectable.
For the generation of most musical waveshapes, the use of some limited number of Fourier components, typically 16 or 32, is sufficient for accurate synthesis of the desired tone. However, for the generation of an ideal sawtooth waveform, it is desirable to include a greater number of harmonics, say 48. This could be implemented by adding another parallel processing channel to the computor organ, to evaluate the 33rd through 48th order Fourier components. However, this solution would add to the cost and complexity of the musical instrument.
Thus, it is an object of the present invention to provide means for extending the harmonic content of a computor organ without utilizing an additional parallel processing channel. Other objects of the present invention include implementing the accurate synthesis of a sawtooth waveform in a computor organ, and the utilization of an appropriately programmed read-only memory to provide extended harmonic information during the generation of such a sawtooth waveform.